1. Field of the Invention
The present application relates to a fan rotor for a turbomachine such as an airplane turboprop or turbojet.
2. Description of the Related Art
A turbomachine fan comprises a disk carrying blades at its outer periphery, the blades having roots that are engaged in substantially axial grooves in the outer periphery of the disk. The blades are held radially on the disk by co-operation between the shapes of their roots and the shapes of the grooves in the disk, the blade roots being of dove-tailed type, for example.
A spacer is interposed between the root of each blade and the bottom of the corresponding groove in the disk to prevent the blade from moving radially in the disk, and at its upstream end the spacer has a nib that extends radially outwards and that presents a downstream radial face forming an axial bearing surface for an upstream radial face of the blade root in order to retain the blade axially in the upstream direction. The spacers ensure that the blades on the disk all have the same axial position so as to avoid creating any unbalance, and they are suitable for bearing axially against an annular cheekplate fastened to the upstream end of the disk.
In the happily-infrequent event of a fan blade being lost or broken, the blade is projected against an adjacent blade, which is then subjected to an upstream axial force that is very violent, with this effect being transmitted to the upstream cheekplate by the corresponding spacer. The spacer comes to bear axially against the cheekplate which is designed to deform elastically in order to damp a portion of this axial force and thus avoid losing other blades of the fan. Axial retaining means for retaining the blades in an upstream direction are also mounted on the disk, downstream from the blades, in order to take up a portion of this axial force in the event of the deformation of the cheekplate reaching a certain threshold.
In the present art, the nib of each spacer is designed to transmit all of the above-mentioned axial force to the upstream cheekplate, and it is subjected to large shear forces in the axial direction while this force is being transmitted. It is therefore necessary for the nib to be overdimensioned in the axial direction so as to enable it to withstand the forces, thereby giving rise to each nib being large in axial size and to an increase in the total weight of the fan rotor.
In order to compensate for the overdimensioning in the axial direction of a spacer nib, it is possible to pare away the upstream end of the corresponding blade root to the same extent. Nevertheless, that solution is unsatisfactory since the blade root then presents an axial dimension that is shorter than the axial dimension of the groove in the disk and runs the risk of exerting high contact forces against the side walls of the groove that can lead to premature wear thereof.